Accessing and listening to computer-network based audio content is currently accomplished by transferring audio content from a computer network, such as the Internet, to an end-user's computer, where the audio content is then played. Until recently, audio content was exclusively stored as a computer file that needed to be completely downloaded to the end-user's computer before it could be played. While the recent development of streaming audio technologies, such as REAL AUDIO®, has provided a measure of concurrency between downloading and playing audio content, a computer with network access is still a required component for retrieving and playing computer-network based audio content.
The process of accessing audio information is composed of many parts. Typically common to all devices is an audio source and multiple clients. When transferring information from an audio source to multiple clients, a number of technologies are typically implemented to make the process more efficient.
One such technology is cache management. Cache management enables enhanced efficiency in the use of bandwidth, so that multiple clients listening to the same information should not have to retrieve it every time from the source.
Normally when downloading audio information, a user downloads from the source to the client and plays the audio from the client side. In a cached environment, the user downloads from the source to a proxy, which caches the information, and from the proxy to the client. It is assumed that the connection between the proxy and the client is better than the connection between the source and the client. An example of a cache management system is Squid (http://www.squid-cache.org).
Another component in servicing audio clients is a streaming server. Streaming is a process by which segments of audio data are transmitted to the client in a way that ensures that the client always has necessary information. A streaming server transmits just the necessary information to the client, for the client to render. At any point in time, the user does not need the complete audio data. For example, when listening to a 3 hour lecture in streaming audio format, the user does not ever need to have the whole 3 hour lecture in memory on the client side. Rather, the user needs only one or two seconds at a time in memory. An example of a streaming audio server is a Real Audio server (www.real.com )
A client receiving a REAL AUDIO® transmission may find that for some reason the connection has gone bad in the middle of the transmission. One thing a REAL AUDIO® server may do to deal with this is to ‘drop off’ packets—by dropping a missed segment and skipping to the next segment. This would be preferable if a user were listening to live radio. Alternatively, the server could continue sending data as if nothing has happened. In each case the user would hear quiet followed by the continued transmission. If packets were dropped, some information would not reach the user.
A third technology used for transferring audio information to the client is multicasting. This technology is employed, for example in an MP3 multicasting server, which multicasts streaming audio. A radio station provides an analog source, which is sent to a radio transmitter and to a transcoder which decodes, mixes and encodes the analog source. A client could be, for example, an Ericsson telephone with an MP3 player attached, as described in: (http://www.ericsson.com/press/mp3player.html),(http://www.ericsson.com/press/telecom99/presskit/mp3.html).
Another technology useful in transferring information from an audio source to multiple clients is Voice Over IP (VoIP). VoIP employs transcoders. A standard telephone may connect to a VoIP Gateway. The VoIP gateway converts the telephone signal into a digital signal, encodes it and sends it through a VoIP Server to another gateway, which decodes it and sends it to another telephone. Two telephones can thus communicate over the Internet. It is also known to employ a PBX to provide radio or MP3 music on hold. This is described, inter alia in (http://www.onholdplus.com/pages/ohp3000.html).